In recent years, along with the rapid popularization of the Internet, the capacity enlargement, more advanced functions, and economization of an optical access system have been demanded. As a method for realizing such a system, the research of a passive optical network (PON) has been advanced. The PON is an optical access communication system advantageous for economization because it can share a transmission path between an equipment at a central office and an optical components at the user's premises by using passive element, such as optical power splitter.
In Japan, there has been currently introduced an economic optical access communication system GE-PON (Gigabit Ethernet (registered trademark)-PON) that shares a throughput of 1 Gb/s level among up to 32 users, by time division multiplexing (TDM).
As a next-generation optical access system that can meet the need for further capacity enlargement, the research and development of a 10 G-EPON of the 10 Gb/s level have been advanced, and this system is a system that can enlarge the capacity by an increase in bit rate of an optical transceiver, while using the same transmission path part as that in the existing GE-PON.
On the other hand, it is considered that capacity enlargement exceeding the 10 Gb/s level is required depending on the services such as a high-definition video service, but further speedup (40 or 100 Gb/s level) in bit rate of a transceiver involves a significant cost increase of the transceiver, and a practical system cannot be obtained, which has been a problem.
As a means for realizing economic capacity enlargement, there is reported a wavelength-variable-type WDM/TDM-PON obtained by giving wavelength variability to an optical transceiver so that an optical transceiver in an equipment at a central office can be gradually added according to a bandwidth requirement, and combining the TDM and wavelength division multiplexing (WDM) (for example, refer to Non Patent Literature 1).